Top roller carriers are generally used as a carrying and loading arm for pairs of top rollers and can be lifted relative to the bottom rollers mounted so as to be secured to the machine.
In drafting systems, it is known to carry out an adaptation, which is necessary for reasons concerning textile technology, to the fibre material or the staple length of the fibre material and, for this purpose, to change the spacing between the clamping lines formed by the pairs of rollers of the drafting system. This spacing is also called the field width. It is known, for this purpose, to configure the top roller carrier for the field width adjustment in such a way that the spacings between the top rollers can be adjusted. German Patent Publication DE 43 35 889 C2, for example, shows a top roller carrier for drafting systems of spinning machines, in which the top rollers are mounted in holders by slides. The slides can be adjusted separately from one another for the field width adjustment, in each case, in the longitudinal direction of the top roller carrier. A holder for top aprons is associated with the apron roller. Configured in the top roller carrier is an elastic hollow body, which is loaded with pressure, pneumatically or alternatively hydraulically. The pressure acts via a base plate of the hollow body on plungers and loads the feed and the output roller and also the apron roller and the holder for the top apron with a force, which presses against the bottom rollers and allows the top rollers to act as pressure rollers.
The German Utility Model G 92 14 598 U1 describes a top apron holder for spinning machine drafting systems with an apron guide, which deflects the top apron and tensions it under the pressure of a spring. The apron guide is held on a central piece of the top apron holder.
A load carrier for drafting systems of spinning machines is known from the generic German Patent Publication DE 39 37 667 A1, in which the axles of the top rollers are each fastened in holders, which can be displaced independently of one another in longitudinal guides of the top roller carrier for the field width adjustment. The drafting system is a three roller drafting system, in which the top rollers are configured as pressure roller twins. The pressure on the top rollers is applied by the holders acting like a spring element because of their shape. The holders are not set up to vary the pressure force.
The holders of the known top roller carriers, as they are described in the above-mentioned documents, have the common drawback that they require a large number of individual parts and require time-consuming field width adjustments that are prone to faults for the apron and output roller.
Swiss Patent Publication CH 656 647 A5 shows an apron drafting system, which is used in a spinning machine and has three pairs of rollers consting, in each case, of top and bottom rollers. The top rollers are held in the top roller carrier, which is arranged so as to be pivotable about a pivot pin with respect to the machine stand.
The box-shaped top roller carrier contains a guide arrangement for the top roller pins. Holding down devices, which are spring-loaded in their longitudinal central region and with which approximately the same gap contact pressure is to be achieved for all the pairs of rollers, engage thereon. The top roller carrying pins are guided for this purpose in guide slots of the top roller carrier. The play always occurring in this case between the top rollers and guide edges counteracts an exact adjustment of the clamping point and leads to wear problems. The spacing of the top rollers from one another in the longitudinal direction of the top roller carrier cannot be changed for this reason. An adjustment of the field widths, such as is necessary during adaptation to the fibre material to be respectively processed, is not possible.
Both British Patent Publication GB 691615 and U.S. Pat. No. 3,256,570 show three-roller drafting systems for spinning machines, in which the top roller carrier has slots which are spaced apart from one another in the longitudinal direction of the top roller carrier for guiding the top roller carrying pins or the axles of top rollers.
It can be inferred from British Patent Publication GB 691615 that, to change the spacing of the top rollers guided by the top roller carrier, the top roller carrier present has to be replaced by a top roller carrier, in which the arrangement or the spacing of the slots differs according to the changed requirements. For a fibre material change mentioned as an example, of cotton to viscose, it is described as sufficient to hold two or three alternatively usable or replaceable top roller carriers in readiness. A replacement of this type of the top roller carrier including disassembly and installation of the top rollers is very laborious.
In the drafting system of U.S. Pat. No. 3,256,570, all three top rollers are carried respectively at their axle ends by a frame-like top roller carrier. The guides of the top roller carrying pins are also affected by play as in the apron drafting system of Swiss Patent Publication CH 656 647 A5 and particularly prone to wear because of the top roller carrier pins co-rotating with the top roller. U.S. Pat. No. 3,256,570 describes how the pivoting up of the top roller carrier can be facilitated in magnetically held top rollers and gives absolutely no indication as to how the spacings apart of the top rollers could be changed. This is also only possible by means of a very laborious replacement of the top roller carrier in the drafting system of U.S. Pat. No. 3,256,570.